A review of Shamosuchus and Paralligator (Crocodyliformes, Neosuchia) from the Cretaceous of Asia.

Turner AH - PLoS ONE (2015)

Bottom Line:
Rugosuchus and Batrachomimus are sister taxa to Paralligator.Paralligatoridae is closely related to Theriosuchus, hylaeochampsids and a speciose Allodaposuchus clade, which together are the sister group of Borealosuchus plus Crocodylia.These results support the presence of a diverse clade in eastern Asia and western North America throughout the Cretaceous with origins in the Late Jurassic.

Affiliation: Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York, United States of America.

ABSTRACTThe crocodyliform Shamosuchus is known from numerous Late Cretaceous localities in southern and eastern Mongolia and fragmentary remains from Uzbekistan. Seven species of Shamosuchus have been named from six localities in Mongolia and three in Uzbekistan. Six species originally described as Paralligator were later referred to Shamosuchus. Only the type species, Shamosuchus djadochtaensis has been examined in detail. Many of the named species of Shamosuchus show striking similarity in size and cranial morphology but most are based on partial remains suggesting that the true species diversity is overestimated. A review of all species referred to Shamosuchus recognizes three valid taxa: Shamosuchus djadochtaensis, S. gradilifrons, and S. major. Shamosuchus sungaricus, S. borealis, and S. karakalpakensis are nomena dubia, whereas S. ancestralis, S. ulgicus, S. tersus, and S. ulanicus are junior subjective synonyms of S. gradilifrons. Phylogenetic analysis of 318 phenotypic characters recovers a Paralligatoridae clade consisting of Shamosuchus, Rugosuchus, Batrachomimus, Glen Rose Form, and Wannchampsus. Shamosuchus is non-monophyletic: S. djadochtaensis is near the base of Paralligatoridae whereas S. gradilifrons + S. major are the most deeply nested. The name Paralligator is resurrected for this clade. Rugosuchus and Batrachomimus are sister taxa to Paralligator. Paralligatoridae is closely related to Theriosuchus, hylaeochampsids and a speciose Allodaposuchus clade, which together are the sister group of Borealosuchus plus Crocodylia. These results support the presence of a diverse clade in eastern Asia and western North America throughout the Cretaceous with origins in the Late Jurassic.

Mentions:
Shamosuchus major was described on the basis of a large, incompletely preserved skull and isolated skull remains from two other individuals. PIN 3726/501 (the holotype) and PIN 3726/502 were collected in 1974 at Khongil Tsav from the Bayanshiree Fm. (Fig. 5A–D). Efimov [8] provided a brief description of S. major citing the poor preservation and incompleteness of the holotype. He noted that it differed from all other species of Paralligator (as it was named at the time) by its large size and the medial contact of the premaxillae posterior to the external naris. Efimov provided no explicit justification for inclusion of these fossils in Paralligator, although the introduction to the paper provides some insight. Here Efimov mentions a set of retained primitive and derived features present in Paralligator. Included in this list is contact between the lacrimal and nasal, frontal participation in the supratemporal fenestra, a greatly elongated secondary choana, and presence of “lateral line” troughs on the skull (what I describe here as an orbitonasal sulcus) (Fig. 11). Efimov specifically mentions these traits to cast doubt on the presumed close affinity between Paralligator and Alligator, but they could easily have been informing his inclusion of other material into Paralligator.

Mentions:
Shamosuchus major was described on the basis of a large, incompletely preserved skull and isolated skull remains from two other individuals. PIN 3726/501 (the holotype) and PIN 3726/502 were collected in 1974 at Khongil Tsav from the Bayanshiree Fm. (Fig. 5A–D). Efimov [8] provided a brief description of S. major citing the poor preservation and incompleteness of the holotype. He noted that it differed from all other species of Paralligator (as it was named at the time) by its large size and the medial contact of the premaxillae posterior to the external naris. Efimov provided no explicit justification for inclusion of these fossils in Paralligator, although the introduction to the paper provides some insight. Here Efimov mentions a set of retained primitive and derived features present in Paralligator. Included in this list is contact between the lacrimal and nasal, frontal participation in the supratemporal fenestra, a greatly elongated secondary choana, and presence of “lateral line” troughs on the skull (what I describe here as an orbitonasal sulcus) (Fig. 11). Efimov specifically mentions these traits to cast doubt on the presumed close affinity between Paralligator and Alligator, but they could easily have been informing his inclusion of other material into Paralligator.

Bottom Line:
Rugosuchus and Batrachomimus are sister taxa to Paralligator.Paralligatoridae is closely related to Theriosuchus, hylaeochampsids and a speciose Allodaposuchus clade, which together are the sister group of Borealosuchus plus Crocodylia.These results support the presence of a diverse clade in eastern Asia and western North America throughout the Cretaceous with origins in the Late Jurassic.

Affiliation:
Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York, United States of America.

ABSTRACTThe crocodyliform Shamosuchus is known from numerous Late Cretaceous localities in southern and eastern Mongolia and fragmentary remains from Uzbekistan. Seven species of Shamosuchus have been named from six localities in Mongolia and three in Uzbekistan. Six species originally described as Paralligator were later referred to Shamosuchus. Only the type species, Shamosuchus djadochtaensis has been examined in detail. Many of the named species of Shamosuchus show striking similarity in size and cranial morphology but most are based on partial remains suggesting that the true species diversity is overestimated. A review of all species referred to Shamosuchus recognizes three valid taxa: Shamosuchus djadochtaensis, S. gradilifrons, and S. major. Shamosuchus sungaricus, S. borealis, and S. karakalpakensis are nomena dubia, whereas S. ancestralis, S. ulgicus, S. tersus, and S. ulanicus are junior subjective synonyms of S. gradilifrons. Phylogenetic analysis of 318 phenotypic characters recovers a Paralligatoridae clade consisting of Shamosuchus, Rugosuchus, Batrachomimus, Glen Rose Form, and Wannchampsus. Shamosuchus is non-monophyletic: S. djadochtaensis is near the base of Paralligatoridae whereas S. gradilifrons + S. major are the most deeply nested. The name Paralligator is resurrected for this clade. Rugosuchus and Batrachomimus are sister taxa to Paralligator. Paralligatoridae is closely related to Theriosuchus, hylaeochampsids and a speciose Allodaposuchus clade, which together are the sister group of Borealosuchus plus Crocodylia. These results support the presence of a diverse clade in eastern Asia and western North America throughout the Cretaceous with origins in the Late Jurassic.